The advent of the high-heeled shoe was as a fashionable dress shoe and, as such, fulfilled its purpose satisfactorily. Due to its appeal, however, over the years, it has evolved into everyday footwear, a purpose for which it was never intended. Put simply, high-heeled shoes and proper biomechanical locomotion are not complementary. High-heeled shoes violate foot physiology and the biomechanics of locomotion.
To begin with, for definitional purposes, high heeled means shoes with heels exceeding 11/2 inches (3.3 cm) in length. With reference to the foot terminology used herein, the anterior is forward (toes), the posterior is rearward (the heel), the interior is medial (instep), the outside is lateral, and the bottom is plantar. The bones are designated, in order from the anterior to posterior, as phalanges (toes), metatarsals, cuneiforms, navicular, tali and calcaneus (heel) while first means medial and fifth means lateral (see FIG. 1). Hence, the first phalange is the medial most phalange bone (big toe). Joints between bones commonly are designated by the names of the two adjoining bones. For example, "the little toe joint" is the fifth metatarsal phalangeal articulation. Finally, when the foot is angled toward the medial axis is referred to as valgus, while toward the lateral axis, as the varus.
The foot inside a high-heeled shoe is held in a different position than a foot which functions in a low-heeled shoe (near normal positioning). This position is referred to as the plantar flexed position or plantar flexion. Plantar flexion describes the foot position where the foot is pointed in a downward direction, with the toes parallel to the floor. When in this position, the foot is unnaturally rigid thereby causing forces normally directed to the heel, to shift to the ball of the foot.
Locomotion, basically, involves a two-phase cycle; a weight bearing and nonweight bearing. When wearing high heels during the weight-bearing phase of the gait cycle, rigidity, as noted above, can produce potentially damaging, forced stretching of the plantar fascia and possible development of heel spurs.
When the foot is held in a plantar flexed (supinated position as described in the literature), it does not allow the body to properly absorb the impact shock generated by contact of the foot with the ground. Due to the absence of shock absorbing ability, the impact force is passed to the body from the foot through the ankle, leg, knee, up the spinal column and, ultimately, to the neck. Hence, the entire vertical skeletal system and associated musculature is affected. More specifically, the shock energy is not physiologically damped as it is in a normal heel-to-toe gait. With the impact force being concentrated on the anterior metatarsal area (ball), the foot often sustains enhanced trauma which is evidenced by a substantial increase of injuries to anterior metatarsal area.
In addition to the above-described deleterious effects, the plantar flexion creates indirect physiological complications. First, increased shock impact forces cause the calf muscles to compensate for the diminished impact damping of the foot by tightening. The tightening and increased strain on the front part of the lower leg are symptomatic of anterior shin splints (inflammation of the front, lower leg) which develop from such muscle strain. Once developed, the body attempts to decrease strain on the legs by increasing strain on the knees, which in turn, tend to flex. The hips also then, flex from the knee flexion. In combination, these reactions cause the body's center of gravity to move forward whereby the buttocks protrude and the back arches to balance the center of gravity and to maintain a standing position. It is readily appreciated that once the back arches, the entire spinal cord extending to the neck, is affected and the chest and buttocks are caused to compensate even more. In short, locomotion in high-heeled shoes creates dynamic, impact deforming forces on the body.
There are three common foot conformations. One is normal and two are deviations; forefoot and rearfoot deformities. Forefoot deformity (see FIG. 2) is generally results in abnormal subtalar joint pronation (greater than 7.degree. forefoot varus). Plantar flexion and increased median arch height are the deforming characteristics caused by wear of high-heeled shoes. Accordingly, when combined, the problems of forefoot deformity are exacerbated where the foot is maintained in an overly rigid configuration and a constant abnormal attitude of propulsion. Thus, the lever-mobile adapter sequence of the normal gait cycle is disrupted.
Turning now to the biomechanical principals involving a normal foot (see FIG. 3) it possesses less than 7.degree. forefoot varus and less than 5.degree. sub-talar eversion (or inversion). The normal foot provides a lever mobile adapter sequence for the gait cycle which provides for normal locomotion, shock impact damping and is compatible with natural skeletal and muscle structure. When a normal foot is exposed to high-heeled shoes, it should be readily appreciated from the foregoing that the plantar flexion coupled with increased median arch height results. Hence, a sufficient degree of pronation, necessary to effect proper weight distribution and shock dissipation, is prevented. This, in turn, causes the discomfort and injury prone conditions of high-heeled shoes.
Finally, rearfoot deformity (see FIG. 4) causes abnormal subtalar pronation. The forefoot valgus at the metatarsal heads (greater than 5.degree. subtalar eversion or inversion) causes the forefoot to turn towards the medial axis (pronation). Normally, the forefoot valgus is approximately 3.degree. and extends from the lateral aspect to the medial aspect along the metatarsal parabola (the curved line defined by the metatarsal phalangeal articulation) and imparts a normal degree of pronation.
It is well known that abnormal or augmented pronation is generally undesirable. (For a more detailed explanation of the deleterious effects of abnormal pronation especially in athletics, reference is made to the inventor's patent application Ser. No. 096,239). Abnormal pronation, caused by a rearfoot deformity, is desirable to compensate for the unnatural biomechanics induced by high-heeled shoes. Since rearfoot deformity induces body weight to be transmitted through the subtalar joint in a shorter period of time, exposure of the metatarsals to those forces is minimized. As a result, there is less time for abnormal subtalar joint pronation to develop when high-heeled shoes are worn.
Previous orthoses for high-heeled shoes have been developed to make the wear more comfortable. Generally, they provide only rigid, stationary support for the foot arches without regarding biomechanical dynamics. For example, a recently issued patent, Brown, U.S. Pat. No. 4,688,338, describes a laminated orthotic for high-heeled shoes. Brown's approach is to provide a multilayered structure of resin impregnated graphite fiber layers where the different layers possess differential geometric orientations relative to the longitudinal axis of the foot. The identified purpose of the structure is to offer a rigid platform resistive to the forces associated with high-heeled shoe wear. In Brody, U.S. Pat. No. 3,068,872 a stiff foot supporting device for a curved elliptical high-heeled (court) shoe is described. That device includes an arch portion for better supporting the arch during locomotion. Although both patents analyzed the abnormal biomechanics of locomotion, they failed to recognize the simple and elegant expedient of inducing pronation to compensate for the artificially induced deformities occasioned by high-heeled shoes.